1. Field of the Invention
This disclosure relates to a backlight unit, and more particularly to a backlight unit configured to implement slimness and reduce its manufacturing costs.
2. Description of the Related Art
Cathode ray tubes (CRTs), which are widely used display devices, are mainly used in TVs or monitors for measuring apparatuses or information terminals. However, the heavy weight and large size of the CRTs have been a major hindrance to the manufacturing of small, light electronic products.
To address this matter, LCD devices are gradually being used in a wide range of applications due to their advantages such as lightness, thinness, and low power consumption. Accordingly, LCD devices are being manufactured to have even larger screens, be thinner, and consume less power. Such LCD devices display images by controlling the amount of light transmitted through liquid crystal.
LCD devices are not self-illuminating display devices, unlike CRTs. As such, an LCD device includes a backlight unit provided on the rear surface of an LCD panel. The backlight unit includes a separate light source providing the light necessary to display an image. The backlight unit is classified as either an edge type or a direct type in accordance with the disposition of its light source.
The edge type backlight unit 10 is configured to include a light source 12, a light guide plate 11, a light source housing 13, and optical sheets 15, as shown in FIG. 1A. The light source 12 is disposed at one side of the edge type backlight unit 10. The light guide plate 11 is configured to disperse incident light from the light source 12. The light source housing 13 is configured to guide light emitted from the light source 12 toward the light guide plate 11. The optical sheets 15 are disposed on the light guide plate 11. The edge type backlight unit 10 further includes a reflection sheet 14 disposed under the light guide plate 11. The reflection sheet 14 is configured to reflect light downward-progressing from the light guide plate 11 toward the optical sheets 15.
The edge type backlight unit 10 enables light generated in the light source 12 to enter into the light guide plate 11 and to be converted into two-dimensional light. The converted two-dimensional light is output toward the optical sheets 15. To rectify this, the edge type backlight unit 10 disperses light toward an upper surface (i.e., the rear surface of an LCD panel) using the light guide plate 11, because the light source 12 is disposed at its one edge. Due to this, the edge type backlight unit 10 has lower brightness than that of the direct type backlight unit, and is difficult to use in a large-sized LCD device.
On the other hand, the direct type backlight unit 20 is configured to include a reflection sheet 24, a plurality of light sources 22, a diffusion plate 21, and optical sheet 25, which are placed in a bottom cover 23, as shown in FIG. 1B. The optical sheets 25 are configured to uniformly diffuse light from the light sources 22. To this end, the optical sheets 25 include a diffusion sheet, a prism sheet, a protective sheet, and others which are disposed on the diffusion plate 21. The diffusion plate 21 is configured to contain a dispersing agent. The plurality of light sources 22 are arranged in fixed intervals under the diffusion plate 21. The reflection sheet 24 is disposed under the plurality of light sources 22.
Such a direct type backlight unit 20 causes a brightness difference between the regions in which the light sources 22 are disposed and those in which the light sources 22 are not. In order to minimize this brightness difference, the direct type backlight unit 20 must maintain a sufficient distance between the light sources 22 and the diffusion plate 21. Therefore, it is difficult to develop an LCD device of a size thin enough to meet the desires of customers when using the direct type backlight unit of the related art.